Electric megaphone



Oct. 26, 1954 SHITETSU KAMIMORI ELECTRIC MEGAPHONE Filed July 13, 1951 INVENTOR 5/1 /75 750 k4M/M0E4 Patented Oct. 26, 1954 ELECTRIC MEGAPHONE Shitetsu Kaminiori, Kamakura, Japan, assignor of one-half to Walter Y. Mihata, Honolulu,

Territory of Hawaii Application July 13, 1951, Serial No, 236,498

1 Claim, 1

This invention relates to megaphones, and more particularly to an electric megaphone.

A main object of the invention is to provide a novel and improved portable public address device similar to a megaphone, said device providing a controlled amount of amplification of the users voice and being simple in construction, easy to handle, and light in weight.

A further object of the invention is to provide an improved electric megaphone device incorporating its own amplifier and power supply, said device involving relatively inexpensive com ponents, being rugged in construction, being compact in size and being arranged so that the volume of sound output and the energization of the device can be controlled by one of the users hands which at the same time supports the rear portion of the megaphone while his other hand may be employed to balance or to support the forward portion of the megaphone.

Further objects and advantages of the inven tion will become apparent from the following description and claim, and from the accompanying drawings, wherein:

Figure 1 is a vertical, longitudinal, cross-sectional view taken through an improved electric megaphone constructed in accordance with the present invention;

Figure 2 is a schematic wiring diagram of the electric megaphone of Figure 1.

Referring to the drawings, the improved megaphone is designated generally at II. The megaphone I I comprises a generally rectangular housing I2 of any suitable rigid material, such as sheet metal, said housing having secured to its lower portion the downwardly and forwardly projecting, hollow casing I3 which is provided with the threaded boss M on its bottom wall. Threadedly engaged with the boss M is the tubular, hollow handle I5, and threadedly engaged on the end of the handle is the cap As shown in Figure l, a flashlight cell i? is contained in the handle I5, the center contact I B of the cell engaging a contact spring I 3 se cured to a terminal 2t rigidly mounted in the center portion of the boss I4 and insulated from the boss by a suitable insulating bushing 2i. The bottom of the flashlight cell I! is engaged by a coil spring 22 positioned between the cell and the cap I 5, as shown in Figure l.

Designated at 23 is a rheostat which is mounted in the rear wall of the casing I3. Secured on the shaft of the rheostat externally adja cent the rear wall of said casing I3 is a control knob '24. Secured to the lower portion of the forward wall of the housing I2 is a control switch 25 comprising a movable armature 25 and a pair of stationary contacts 27 and 28. The armature 26 is normally out of contact with the elements 2'! and 28. Designated at 25; is a lever pivoted to the casing I3 and depending from the casing, as shown in Figure 1. The lever 29 extends adjacent the forward wall surfaces of easing I3 and handle E5, the upper end of the lever 29 being formed with a projection 39 arranged to engage the armature 25 responsive to clockwise rotation of the lever, as viewed in Figure 1, and to move said armature 26 into simultaneous contact with the stationary contact elements 2'! and 28. It will be apparent from Fig ure 1 that when the handle I! is grasped by the users hand, the volume control knob 24 may be manipulated by the users thumb while the lever 29 may be rotated by one of the users fingers while substantially maintaining grip on the handle I5.

Secured to the rear wall of the housing I2 is a conventional microphone 3i which is provided with the usual centrally apertured cover 32 through which sound input energy may be directed to the active portion of the microphone. Mounted inside the housing I2 is an amplifier 33 of conventional construction whose plate circuits are energized by a battery 34 also mounted in the housing I2 adjacent the amplifier 33. The filament circuits of the amplifier 33 are energized by the flashlight cell I l, as will be presently described.

Secured to the forward wall of the housing I2 is a sound-reproducing unit 35 which is generally conventional in construction and which comprises a flaring horn 36 in which are secured the respective concentric bafiie units 31 and 38, the inner baffie unit 38 being connected to and communicating with the sound output conduit 39 of a conventional electromagnetic sound reproducer 40, preferably of the permanent magnet type. Depending from the bottom surface of the horn 36 is a lug M to which is pivotally se cured the handle 42, the pivotal connection being shown at 43 and being located so that the handle 42 may be rotated from a position adjacent the surface of the horn to a position extending substantially at right angles to the axis of said horn, as shown in Figure 1, the forward top corner of the handle 42 abutting the horn to limit counterclockwise rotation of said handle beyond the position thereof shown in Figure 1..

Secured to the lower rear portion of the housing I2 is a first ring M, and similarly secured to the forward portion of the horn 35 is a second ring 45, said rings being employed for connection to the ends of a suitable shoulder strap, not shown.

Referring now to Figure 2, it will be seen that the amplifier 33 may comprise an input transformer 46, the microphone 3! and the volume control 23 bein connected in series with the primary winding 4'! of said transformer. The opposite terminals of the secondary 48 of the transformer are connected to respective control grids 49 and 59 of amplifier tubes and 52. The center tap of the secondary 48 of the transformer is connected by a wire 53 to the negative terminal of the battery 34. Connected between the switch terminal 28 and said negative terminal is a grid resistor 54. The flashlight cell I1 is connected between the switch terminal 2'1 and ground, as shown. The filaments of the tubes 5| and 52 are wired in parallel, said filaments being of the center tap type, the center tap of the filaments being grounded by a wire 55. The outer terminals of the filaments are connected by a wire 55 to the switch armature 29. Designated at 51 is an output transformer having a primary 58'and a secondary 59,. The respective plates 69 and 6| of tubes 51 and .52 are connected to the respective end terminals of the primary 58. The center tap of the primary 58 is con nected to the respective screen elements 52 and 63 of the tubes 5| and 52, said center tap being connected by a wire 54 to the positive terminal of the battery 34, as shown. The electromagnetic sound-reproducing member 49 is connected to the terminals of the secondary of out put transformer 51.

It will be readily apparent that the circuit illustrated in Figure 2 is a conventional push-pull amplifier circuit, and that the circuit is normal ly deenergized, inasmuch as the armature is normally out of contact with the contact elements 21 and 28, as shown in Figure 2. When the armature 26 is depressed to engage the contacts 2! and 28, the filaments of the tubes 51 and 52 are energized from the battery l'l through contact 21, armature 26, wire 56, and said filaments, and at the same time the plate-cathode circuits of the tubes are completed from the negative terminal of battery 34 through resistor 54, contact 28, armature 26, wire 55 and the filaments of the tubes 5| and 52. Therefore, when sound energy impinges on the active element of the microphone 3|, said sound energy will induce voltages in the primary circuit of the transformer 46, inasmuch as the primary circuit has direct current furnished thereto by the battery I! through contact '21, armature 26, wire 55, and a wire 95 connecting wire 55 to the terminal of primary 47 opposite to that to which the microphone 5| is connected, as shown in Figure 2. The sound energy acts onthe microphone to produce fluctuations of the current in the primary of the transformer 46, said fluctuations being inductively transmitted to the secondary 48 and thence to the amplifier tubes 5! and 52 by input grids 49 and 50' in the well known manner. The output signals of the amplifier tubes 5! and 52 are impressed on the primary 58 of the output transformer 51 and thence delivered by the secondary winding of said transformer to the electromagnetic sound reproducer 49. The gain of the system may be regulated by adjusting the volume control 23, namely, by regulating the amount of current in the primary circuit of the input transformer 46.

In using the device, the operator grips the handle I! with one hand and supports the forward portion of the megaphone by holding the handle 42 with his other hand. To energize the megaphone, the operator engages the lever 29 with a finger of said hand and rotates said lever clockwise, as viewed in Figure 1. At the same time, the gain of the system may be regulated by rotating the knob 24 with the thumb of the hand which at the same time grips the handle l1. When the lever 29 is released, the armature 26 of switch 25 returns to its open position, since said armature is spring biased in a conventional manner to its open position. Therefore, upon relaxation of pressure on the lever 29, the filament and plate-cathode circuits of the amplifier tubes 5| and 52 are opened, completely deenergizing the megaphone.

The amplifier tubes 5! and 52 may be of any suitable battery-operated type, such as 334 tubes, the flashlight cell I! being of the ordinary type, and the plate battery 34 being a conventional 6'7 -volt, small dry battery, such as is commonly employed in portable radio receivers.

The top of the housing l2 comprises a removable cover 65 which may be normally secured in overlying relationship to the housing by any suitable detachable fastening means, and which may be readily removed to provide access to the interior of the casing l2 .for replacement of tubes or batteries, or for other required repairs.

While a specific embodiment of an improved electric megaphone has been disclosed in the foregoing desoription, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claim.

What is claimed is;

In a megaphone, a housing, a flaring horn se cured to one end of said housing, a microphone secured to the other end of said housing, a sound reproducer mounted in said housing and communicating with said horn, an amplifier in said housing, means connecting the output cir-- cuit of said amplifier to said sound reproducer, means connecting said microphone to the input circuit of said amplifier, a depending substantially straight hollow handle secured to the bottom of said housing between the micro-- phone and the horn, a battery in said handle, contact means in said handle engaging the ter minals of the battery, a switch in the lower forward portion of the housing, said switch including a stationary contact element and a movable contact element, an arm pivoted to the bottom portion of said housing and being engageable with said movable contact element to close said switch responsive to rotation of said arm, said arm being provided with an actuating element for rotating the arm depending from the housing and disposed forwardly adjacent the upper portion of said handle, circuit means connecting the battery to said amplifier and including said switch, a volume control mounted on the upper portion of the rear side of said handle substantially opposite said actuating element, and means controllingly connecting said volume control to said amplifier, whereby an operator may grip the handle with one hand, operate the actuating element with one finger of said hand, and simulta- I neously actuate the volume control with the thumb of said hand.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,207,705 Cox July 16, 1940 2,218,389 Warmbier Oct. 15, 1940 2,314,108 Silverman Mar. 16, 1943 2,505,551 Knowles Apr. 25, 1950 

